This is what i can see.
The authcab file(s) (eg %windir%/SoftwareDistribution/AuthCabs/authcab.cab) contain an XML file called 'authorization'. There seems to be one for windows update and one for Microsoft update if you have that installed.
There is an element in this file called ExpiryDate which states:
<ExpiryDate>2017-12-03T11:59:25.5067616-08:00</ExpiryDate>
which depending on your timezone is more or less now.
This lines up with an error from windowsupdate.log namely
DtaStor FATAL: Service 7971F918-A847-4430-9279-4A52D1EFE18D requested, but it is expired
where that guid relates to MS Update.
Hopefully this means we simply have to wait for MS to update the, er, updater so it will have a new expiry date! I believe in a perfect world the updater will do this automatically once one becomes available. Otherwise hopefully we are supplied with a download link somewhere.